Solar light collecting and guiding system

ABSTRACT

This invention presents a solar light collecting and guiding system for stabilizing the output light intensity, wherein the system comprising an array of converging lenses and optical fibers for collecting light focused by converging lenses. The fibers and the lenses are in one-to-one correspondence wherein the input end of an optical fiber is located in the focus position of the corresponding converging lens, and the axis of the optical fiber overlaps with the principal axis of the corresponding converging lens. The system is equipped with a sunlight tracking positioning device for synchronized motion, wherein the device is applied to tracking the sun light ray vertical incident into the central converging lens. The system has the function of outputting stable light intensity, that is, it can effectively reduce the variation of the collecting efficiency caused by the positioning deviation between the incident angle of sunlight and the designed input angle.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Stage Application of InternationalPatent Application No. PCT/CN2018/080111, filed on Mar. 23, 2018, whichclaims priority to Chinese Patent Application No. 201810186119.0, filedon Mar. 7, 2018, the contents of each of which is incorporated herein byreference in its entirety.

FIELD OF THE INVENTION

The invention relates to the field of solar energy utilization, inparticular to a solar light collecting and guiding system.

BACKGROUND OF THE INVENTION

In systems such as solar concentrators, it is generally necessary toconverge the solar through a lens system, so as to input into thetransmission medium with a small cross-sectional area, such as anoptical fiber. Since the size of lens is limited by the manufacturingprocess and the size of the spot, a plurality of converging lenses areusually used to enhance the intensity of the concentrated light. In thecase of a non-tracking lens system, as disclosed in the publication No.JPH02239505A, a 3-branch type light collecting device fixed in threedirections such as east, west and south is disclosed, the utilizationrate of the lenses is low.

In some non-tracking systems, sunlight is collected by differentconverging lenses in different time periods, resulting in low lensesutilization and increased system cost. In order to improve the lightefficiency of converging focused by the lenses, the solar trackingmechanism of a system is usually used to locate and track the sun. Inthis way, all the converging lenses are synchronously positioned, sothat they can collect more sunlight and achieve high convergingefficiency.

Because of the small area of the light spot focused by lenses, thepositioning accuracy of the existing solar tracking device can reach 1°or less, but even so, the error generated will affect the intensity oflight coupled into the fiber. Even if it has been perfectly positioned,since the relative motion of the sun and the earth is continuous, thedeviation angle of the incident parallel solar rays and the plane of thelens gradually increases with time, causing the focused spot to deviate,which will result in part of the sunlight cannot be coupled into thefiber, thereby reducing the coupling efficiency of sunlight. For thisreason, the solar tracking positioning device must frequently track thesun and rotate the convergence system. Equipped with a solar trackingand positioning device, such as the patent of U.S. Pat. No. 4,477,145,the lenses of the convergence array are arranged on the same plane, thatis, the coupling efficiency of each lens changes the same. Therefore,the coupled light of each lens will experience the same amount ofintensity change when there is deviation of tracking and positioning.

In many cases, there are strict requirements on the concentrated lightintensity stability. For example, when the concentrated sunlight isapplied to illumination, since the human eye is more sensitive tochanges in light intensity, frequent changes in light intensity maycause discomfort. To this end, effective measures are needed to reducethe amount of change in the total intensity over time, therebymaintaining the light intensity of the fiber output at a relativelystable level. This requires the tracking and positioning device in thesystem to have high positioning accuracy and the position must becontinuously corrected in a short time interval to ensure that thesunlight intensity remains at a relatively stable level. It results invery high precision requirements for tracking and positioning equipment,and places higher demands on the quality of the system's converginglenses in terms of manufacturing and installation. In addition, frequentpositioning and rotation systems increase the complexity of the systemand the difficulty of control.

SUMMARY OF THE INVENTION

This invention provides a solar light collecting and guiding systemwhich is able to stabilize the light power collected into the opticalfibers.

Herein presents a solar light collecting and guiding system, wherein thesystem comprising an array of converging lenses, optical fibers, and asunlight tracking positioning device, which are listed as follows:

1. An array of converging lenses for collecting sunlight into opticalfibers, wherein the array is composed of (2n_(x)+1)×(2n_(y)+1)converging lenses arranged in the east-west direction and thenorth-south direction, where the number of rows and columns of theconverging lenses are 2n_(x)+1, and 2n_(y)+1 respectively, where bothn_(x) and n_(y) are positive integer no less than 2; wherein the centersof the converging lenses of the same row or the same column are locatedin a circle, and the principal axes of the converging lenses intersectsthe circle center; and

2. Optical fibers for collecting light focused by converging lenseswherein the input end of an optical fiber is located in the focusposition of the corresponding converging lens, and the axis of theoptical fiber overlaps with the principal axis of the correspondingconverging lens;

3. A sunlight tracking positioning device, wherein the sunlight trackingpositioning device is applied to tracking the sun light ray verticalincident into the central converging lens, and the array of converginglenses and optical fibers move synchronously with the trackingpositioning device.

The numbers of converging lenses of the array satisfies the conditionsof

${{\tan^{2}\left( {n_{x}\delta_{x}} \right)} + {\tan^{2}\left( {n_{y}\delta_{y}} \right)}} < \left( \frac{R + r}{f} \right)^{2}$where δ_(x) is the angle between the principal axes of two adjacentconverging lenses in each row of converging lenses, and δ_(y) is theangle between the principal axis of two adjacent converging lenses ineach column of converging lenses, R is the radius of the core of thefiber, r is the radius of the light spot of the sunlight concentrated bythe converging lens, f is the focal length of the converging lens.

According to the invention, all the converging lenses are of the sametype and having the same size and focal length. All the optical fibersare of the same type and having the same core radius and numericalaperture.

The focal length of the converging lens should meet the condition of

$f \geq {\frac{D}{2}\sqrt{\frac{1}{NA} - 1}}$where NA is the numerical aperture of the optical fiber and D is thediameter of the converging lens.

The focal length of the converging lens should meet the condition of

${\frac{{1.2}D}{2}\sqrt{\frac{1}{NA} - 1}} \geq f$

The radius of the light spot of the sunlight r concentrated by theconverging lens should not be greater than the radius of the fiber coreR, that is, r≤R.

The angle between the two adjacent converging lenses in the converginglens array should meet the condition oftan²(n _(x)δ_(x)+β)+tan²(n _(y)δ_(y)+β)≤tan²(ω_(e))where β is the maximum angle between the sunlight ray and the axis ofthe central converging lens owing to tracking positioning error, themaximum incident deviation angle ω_(e) is the angle between the sunlightray and the principal axis of the converging lens when the minimumcoupling efficiency η for the central converging lens allowed by thesystem is reached, wherein the maximum incident deviation angle ω_(e)and the minimum coupling efficiency η of the central converging lensmeet the condition of

$\eta = {1 - \frac{{r^{\; 2}\left( {\varphi - {\sin\;{\varphi cos\varphi}}} \right)} - {R^{2}\left( {\theta - {\sin\;{\theta cos}\theta}} \right)}}{\pi r^{2}}}$${{{wherein}\mspace{14mu}\theta} = {{arc}\;\sin\frac{d_{e}^{2} + R^{2} - r^{2}}{2d_{e}R}}},{\varphi = {\arcsin\left( {\frac{R}{r}\sin\;\theta} \right)}},{d_{e} = {f \times \tan\;\left( \omega_{e} \right)}},$where d_(e) is the lateral offset of the light spot on the focal planewhen the angle between the incident ray and the principal axis of theconverging lens varies from zero to the maximum deviation angle.

For an array of converging lens arranged in a plane, factors such astracking error, the movement of the sun, will causing the variation ofconverging efficiency with time, such variation will lead to unstableoutput for application such as lighting, and laser pumping. The systemof this invention can effectively reduce the variation of the convergingefficiency of the system caused by such errors, and can still ensurehigh converging efficiency of the system even when the positioning andtracking system is working with a relatively large positioning error.Therefore, it is able to effectively stabilize the output lightintensity, which is realized by adopting a non-planar arrangement of theconverging lenses array, strictly controlling the angular relationshipof the adjacent converging lenses and the number of the converginglenses, and matching the parameter relationship between the opticalfiber and the lenses.

The robust output light intensity characteristic of the invented systemis realized by slightly reducing the coupling efficiency of theconverging lenses except the central converging lens. Such design leadto large tolerance to positioning error. In addition, all the converginglenses can work with relatively large coupling efficiencies even whenthere is relatively large positioning error of the system.

The invented system allows the tracking and positioning device to have acertain angular positioning error. The output light intensity is notsensitive to small changes in the angle of incident sunlight. Therefore,it allows a long tracking and positioning interval time, reducing thesystem complexity and energy consumption caused by frequent tracking androtating system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of the convergence light guidingarrangement system of the present invention, where a row of convergencelens and the corresponding optical fiber are presented.

FIG. 2 is a schematic diagram of fully coupled matching principle.

FIG. 3 is a schematic diagram of lateral error of light spot.

FIG. 4 is a schematic diagram of sunlight incidence at differentconditions, with (a) sunlight vertically incident on the center lens,and (b) sunlight incident with an angle with the axis of the centerlens.

FIG. 5 is a schematic diagram of relationship between couplingefficiency and sunlight incident angle.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention will be further described below in conjunction with thedrawings and specific embodiments, but the scope of protection of theinvention is not limited thereto.

The lenses group located on the same plane is sensitive to the angulardeviation, that is, when there is an incident deviation-angle, theamount of light coupled into the optical fiber changes greatly when itis incident perpendicularly to the sunlight. Thus, a solar lightcollecting and guiding system that stabilizes the intensity of sunlightoutput is designed for the invention, including a converging lensesarray and optical fibers 2. The converging lenses array is composed of(2n_(x)+1)×(2n_(y)+1) converging lenses 1 arranged in the east-westdirection and the north-south direction, where the number of rows andcolumns of the condenser lenses are 2n_(x)+1, and 2n_(y)+1 respectively,where both n_(x) and n_(y) are positive integer no less than 2; whereinthe centers of the converging lenses 1 of the same row or the samecolumn are located in a circle, and the principal axes of the converginglenses 1 intersects the circle center. And optical fibers 2. forcollecting light focused by converging lenses 1 wherein the input end ofan optical fiber 2 is located in the focus position of the correspondingconverging lens, and the axis of the optical fiber 2 overlaps with theprincipal axis of the corresponding converging lens 1;

The solar light collecting and guiding system is provided with atracking positioning device, and the positioning object of the trackingpositioning device is a central converging lens 1 in the sunlight andthe converging lens array, and solar light collecting and guiding systemfollows the tracking positioning device to move synchronously. As shownin FIG. 1, the sunlight passes through the converging lens array andthen converges into the corresponding optical fiber for transmission,and when the solar vertical plane mirror is incident, the light is justcompletely coupled into the optical fiber 2. The numbers of converginglenses of the array satisfies the conditions of

${{\tan^{2}\left( {n_{x}\delta_{x}} \right)} + {\tan^{2}\left( {n_{y}\delta_{y}} \right)}} < \left( \frac{R + r}{f} \right)^{2}$where δ_(x) is the angle between the principal axes of two adjacentconverging lenses in each row of converging lenses, and δ_(y) is theangle between the principal axis of two adjacent converging lenses ineach column of converging lenses, R is the radius of the core of thefiber, r is the radius of the light spot of the sunlight concentrated bythe converging lens, f is the focal length of the converging lens.

In embodiments, all the converging lenses are of the same type andhaving the same size and focal length. And all the optical fibers are ofthe same type and having the same core radius and numerical aperture. Ascan be seen from the principle of full coupling matching in FIG. 2, theradius r of the converging spot of the parallel sunlight passing throughthe converging lens 1 should not be greater than the radius R of thecore 4, that is, r≤R.

At the same time, the focal length of the converging lens 1 should meetthe condition of:

$f \geq {\frac{D}{2}\sqrt{\frac{1}{NA} - 1}\mspace{14mu}{and}\mspace{14mu}\frac{{1.2}D}{2}\sqrt{\frac{1}{NA} - 1}} \geq {f.}$And the optical power coupled into the fiber is proportional to the areaof the overlap of the light spot and the core 4. Although the solar beamconcentrated by the concentrating device satisfies the requirements ofthe coupling condition of the light and the fiber to some extent, Whenthe center of the concentrated light spot of the sun fails to align withthe central axis of the core 4, part of the light will leak into thesurrounding environment during the coupling and further causing loss oflight as shown in FIG. 3. The lateral error, the maximum incidentdeviation angle ω_(e) and the minimum coupling efficiency η of thecentral converging lens meet the condition of

${{\eta = {1 - \frac{{r^{\; 2}\left( {\varphi - {\sin\;{\varphi cos\varphi}}} \right)} - {R^{2}\left( {\theta - {\sin\;{\theta cos}\theta}} \right)}}{\pi r^{2}}}};}$${wherein},\mspace{20mu}{\theta = {{arc}\;\sin\frac{d_{e}^{2} + R^{2} - r^{2}}{2d_{e}R}}},{\varphi = {\arcsin\left( {\frac{R}{r}\sin\;\theta} \right)}},{d_{e} = {f \times \tan\;{\left( \omega_{e} \right).}}}$And de is the lateral offset of the light spot on the focal plane whenthe angle between the incident ray and the principal axis of theconverging lens varies from zero to the maximum deviation angle. β isthe maximum angle between the sunlight ray and the axis of the centralconverging lens owing to tracking positioning error.

The maximum incident deviation angle ω_(e) is the angle between thecorresponding incident ray and the principal axis of the converging lens1 when the single converging lens 1 reaches the minimum couplingefficiency η allowed by the system. After the above definition, it canbe ensured that when the sun is tracking within this precision range,when the sunlight is incident on the center lens, all the lenses in thearray can collect the light and couple into the corresponding fiber 2.

Obviously, when the incident light is deviated from the principal axisof the converging lens 1, the coupling efficiency of the converging lens1 is lowered. As shown in FIG. 4a , when the sunlight is perpendicularlyincident on the central converging lens, the coupling efficiency of theother converging lenses is reduced due to the presence of the incidentdeviation angle. However, when the angle between the principal axis ofthe adjacent two converging lenses is small, the influence on the totalcoupling efficiency is not large. However, if there is a small deviationangle between the sunlight and the central converging lens 1, as shownin FIG. 4b , on the contrary, the coupling efficiency of the partialconverging lenses 1 may be improved. Thus, the total convergingefficiency of all of the converging lenses can be kept at a relativelystable level. It can be seen that the more the number of converginglenses, the higher the stability of the coupling efficiency.

The following embodiments are based on the above technical means andrequirements. The optical fiber 2 with a radius of 3 mm is used as atransmission medium, and the converging lens 1 with a light spot radiusof 3 mm and a focal length of 100 mm is used to converge the sunlight.FIG. 5 is a schematic diagram of relationship between optical couplingefficiency η and incident angle co. It can be seen that η and ω arenegatively correlated. Taking n-block lenses 1 as a reference for a row(column), the incident solar rays are coupled into the optical fiber 2by a unit number of converging lenses 1. If the incident solar rays areparallel to the main axis of the converging lens 1, the couplingefficiency is 100%. When the n-block converging lenses 1 is in the sameplane, the coupling efficiency is up to n×100%, which is set as the basecoupling efficiency.

Embodiment 1

The seven converging lenses 1 are arranged in one row or one column. Ifthe converging lenses 1 are in the same plane, the coupling efficiencyis up to 7×100%, that is, the basic coupling efficiency is 700%. In thebehavior example, if the converging lenses 1 system of the inventionsets the center plane angle of the adjacent converging lens 1 to beδ_(x)=0.5°, In the initial state, when the incident solar ray isparallel to the central converging lens 1 principal axis, the maximumcoupling efficiency is reduced but it can also reach 688.8848%. When theincident deviation-angle is 0.5°, the coupling efficiency of theconverging system of this embodiment is reduced to 687.9568%, and thevariation due to the incidence angle of sunlight is only 0.9280%. Forcomparison, the parameters and the number of the lenses 1 are given thesame as in the present embodiment, but the converging lenses arearranged on the same plane. In this case, under the influence of theincident angle of 0.5°, the efficiency is reduced to 693.5181%. Theamount of change before and after reached 6.4819%. When the incidentdeviation-angle is 3°, the coupling efficiency of the concentratingsystem of this embodiment is reduced to 660.9971%, and the variation dueto the incidence angle of sunlight is 27.8877%. The convergence systemof the same plane is under the influence of 3° incident angle, theefficiency is reduced to 661.0259%, and the amount of change reaches38.9741%.

Embodiment 2

The seven converging lenses 1 are arranged in one row or one column. Ifthe converging lenses 1 are in the same plane, the coupling efficiencyis up to 7×100%, that is, the basic coupling efficiency is 700%. In thebehavior example, if the converging lenses 1 system of the inventionsets the center plane angle of the adjacent converging lens 1 to beδ_(x)=1°, In the initial state, when the incident solar ray is parallelto the central converging lens 1 principal axis, the maximum couplingefficiency is reduced but it can also reach 688.8848%. When the incidentdeviation angle is 0.5°, the coupling efficiency of the convergingsystem of this embodiment is reduced to 676.8153%, and the variation dueto the incidence angle of sunlight is only 0.9301%. For comparison, theparameters and the number of the lenses 1 are given the same as in thepresent embodiment, but the converging lenses are arranged on the sameplane. In this case, under the influence of the incident angle of 0.5°,the efficiency is reduced to 693.5181%. The amount of change before andafter reached 6.4819%. When the incident deviation angle is 1.5°, thecoupling efficiency of the concentrating system of this embodiment isreduced to 673.0773%, and the variation due to the incidence angle ofsunlight is 4.6680%. The convergence system of the same plane is underthe influence of 1.5° incident angle, the efficiency is reduced to680.5449%, and the amount of change reaches 19.4551%.

It can be seen from the above analysis that since the angle between thesun ray and the principal axis of the converging lenses 1 has a largeinfluence on the conventional converging system, frequent tracking androtating converging systems are required. Since the sunlight isdeflected by about 15° per hour, it is deflected by 1° every 4 minutes.From the above analysis, in this embodiment, even when the incidentdeviation angle is 1.5°, the amount of change in output light intensityis still smaller than that of the convergence system of the same planeat an incident angle of deviation of 0.5°. Therefore, the embodiment canallow the tracking error of the tracking device to reach 0.5°, and canbe repositioned for up to 4 minutes, and the variation of the outputlight intensity does not exceed 4.680%. Thereby, the system complexityand energy consumption brought by the frequent tracking and rotatingconcentrating system are avoided, and the purpose of stabilizing theoutput light intensity is achieved.

Embodiment 3

The nine converging lenses 1 are arranged in one row or one column. Ifthe converging lenses 1 are in the same plane, the coupling efficiencyis up to 9100%, that is, the basic coupling efficiency is 900%. In thebehavior example, if the converging lenses 1 system of the inventionsets the center plane angle of the adjacent converging lens 1 to beδ=0.5°, In the initial state, when the incident solar ray is parallel tothe central converging lens 1 principal axis, the maximum couplingefficiency is reduced but it can also reach 881.4702%. When the incidentdeviation angle is 0.5°, the coupling efficiency of the convergingsystem of this embodiment is reduced to 880.5409%, and the variation dueto the incidence angle of sunlight is only 0.9294%. For comparison, theparameters and the number of the lenses 1 are given the same as in thepresent embodiment, but the converging lenses are arranged on the sameplane. In this case, under the influence of the incident angle of 0.5°,the efficiency is reduced to 891.6662%. The amount of change reaches8.3338%. When the incident deviation angle is 1°, the couplingefficiency of the concentrating system of this embodiment is reduced to877.7524%, and the variation due to the incidence angle of sunlight is3.7178%. The convergence system of the same plane is under the influenceof 1° incident angle, the efficiency is reduced to 883.3293%, and theamount of change reaches 16.6707%.

The embodiments are a preferred embodiment of the invention, but theinvention is not limited to the embodiments described above. Any obviousmodifications, substitutions or variations that can be made by thoseskilled in the art without departing from the scope of the invention arethe scope of the invention.

What is claimed is:
 1. A solar light collecting and guiding system,comprising: an array of converging lenses for collecting sunlight intooptical fibers; the optical fibers for collecting sunlight focused bythe array of converging lenses; and a sunlight tracking positioningdevice, wherein the array of converging lenses is composed of(2n_(x)+1)×(2n_(y)+1) converging lenses arranged in the east-westdirection and the north-south direction, wherein the number of rows andcolumns of the converging lenses are 2n_(x)+1, and 2n_(y)+1respectively, wherein both n_(x) and n_(y) are positive integer no lessthan 2, wherein the centers of the converging lenses of the same row orthe same column are located in a circle, and the principal axes of theconverging lenses intersects the circle center; wherein the input endsof the optical fibers are located in the focus position of thecorresponding converging lens, and the axes of the optical fibersoverlap with the principal axis of the corresponding converging lens;wherein the sunlight tracking positioning device is applied to trackingthe sun light ray vertical incident into the central converging lens,and the array of converging lenses and optical fibers move synchronouslywith the tracking positioning device; wherein the numbers of converginglenses of the array satisfies the conditions of${{{\tan^{2}\left( {n_{x}\delta_{x}} \right)} + {\tan^{2}\left( {n_{y}\delta_{y}} \right)}} < \left( \frac{R + r}{f} \right)^{2}},$where δ_(x) is the angle between the principal axes of two adjacentconverging lenses in each row of converging lenses, and δ_(y) is theangle between the principal axis of two adjacent converging lenses ineach column of converging lenses, R is the core radius of the opticalfibers, r is the radius of the light spot of the sunlight concentratedby the converging lens, and f is the focal length of the converginglens.
 2. A solar light collecting and guiding system as claimed in claim1, wherein all the converging lenses are of the same type and having thesame size and focal length.
 3. A solar light collecting and guidingsystem as claimed in claim 1, wherein all the optical fibers are of thesame type and having the same core radius and numerical aperture.
 4. Asolar light collecting and guiding system as claimed in claim 1, whereinthe focal length of the converging lens should meet the condition of$f \geq {\frac{D}{2}\sqrt{\frac{1}{NA} - 1}}$ where NA is the numericalaperture of the optical fibers and D is the diameter of the converginglens.
 5. A solar light collecting and guiding system as claimed in claim4, wherein the focal length of the converging lens should meet thecondition of ${\frac{{1.2}D}{2}\sqrt{\frac{1}{NA} - 1}} \geq {f.}$
 6. Asolar light collecting and guiding system as claimed in claim 1, whereinthe radius of the light spot of the sunlight r concentrated by theconverging lens should not be greater than the core radius of theoptical fibers R, that is, r≤R.
 7. A solar light collecting and guidingsystem as claimed in claim 1, wherein the angle between the two adjacentconverging lenses in the converging lens array should meet the conditionoftan²(n _(x)δ_(x)+β)+tan²(n _(y)δ_(y)+β)≤tan²(ω_(e)) where β is themaximum angle between the sunlight ray and the axis of the centralconverging lens owing to tracking positioning error, the maximumincident deviation angle ω_(e) is the angle between the sunlight ray andthe principal axis of the converging lens when the minimum couplingefficiency η for the central converging lens allowed by the system isreached, wherein the maximum incident deviation angle ω_(e) and theminimum coupling efficiency η of the central converging lens meet thecondition of$\eta = {1 - \frac{{r^{\; 2}\left( {\varphi - {\sin\;{\varphi cos\varphi}}} \right)} - {R^{2}\left( {\theta - {\sin\;{\theta cos}\theta}} \right)}}{\pi r^{2}}}$${{{wherein}\mspace{14mu}\theta} = {{arc}\;\sin\frac{d_{e}^{2} + R^{2} - r^{2}}{2d_{e}R}}},{\varphi = {\arcsin\left( {\frac{R}{r}\sin\;\theta} \right)}},{d_{e} = {f \times \tan\;\left( \omega_{e} \right)}},$where d_(e) is the lateral offset of the light spot on the focal planewhen the angle between the incident ray and the principal axis of theconverging lens varies from zero to the maximum deviation angle.